As fewer and fewer smartphones, tablets and computers feature 3.5 mm jacks, using headphones increasingly requires the use of adapters and DACs with integrated headphone amplifiers. The alternative, of course, is to use headphones and earphones with a DAC directly integrated in the cable – which is exactly what the Hidizs ST2 Pro Nebula are. They are made for modern smartphones which only come with a USB-C port, so they offer a corresponding USB-C connector.
Disclaimer: I received a unit directly from Hidizs, whom I thank. The ST2 Pro Nebula retail for $69.99. Additional information on the manufacturer’s website.
TL;DR: recap
| Pros |
Cons |
| + The cable integrates a DAC
+ Comfortable + Decent sound signature + Good value for the price |
– Almost no passive isolation
– Too loud |
Rating: 7.5/10
Packaging & Accessories
The box includes the earphones themselves complete with their cable, as well as a set of silicone eartips in three sizes and a faux leather pouch to keep the earphones when not in use.
Design & Comfort
The Hidizs ST2 Pro Nebula sport the classic IEM design, with a roughly triangular shell shape and an over-the-ear, hook-shaped cable. The shells are made of transparent plastic which shows everything inside – as well as how cleanly the earphones are wired. The nozzles are made of metal, and the faceplate has a small metal circle which sports the Hidizs logo. It is overall quite plain, which contributes to making the ST2 Pro Nebula relatively anonymous – in a good way, as they are not dazzling.
Build quality is quite high, and I can’t really find any faults with the earphones.
Thanks to the small size, light weight and rounded shape, I found the ST2 Pro Nebula to be quite comfortable. I can wear them for a couple of hours and still barely realise that I am wearing them, which is definitely a huge plus. They re small enough that even people with smaller ears shouldn’t have any issues fitting them in.
In terms of passive isolation, the ST2 Pro Nebula offer very little: even with foam tips, they just allow most sounds from the outside world to creep in, making it difficult to listen to music in noisy environments such as public transport or a plane.
Speaking of which, the peculiarity of the ST2 Pro resides in the fact that they come with a cable that integrates a DAC and offers a USB-C connector, which is somewhat of a rarity. This makes it possible to use the earphones with modern smartphones and tablets which now normally do not feature a headphone jack. The USB-C housing is made of metal and it features transparent windows on both sides which showcase the chips inside. It is remarkable how miniaturised everything is! The cable itself is made of two twisted cores, each individually sleeved in fabric. There is also a microphone (which however only really works in a quiet environment) with a single button on the right hand side. The cable is quite malleable and lightweight, which makes it pleasant to use.
Extra Features
Contrary to traditional earphones, the Hidizs ST2 Pro Nebula feature an integrated DAC. The ESS Sabre ES9281AC Pro DAC supports PCM streams up to 32 bit and 384 kHz, DSD up to DSD128 and MQA. It offers 70 mW power output, which is more than enough for the vast majority of earphones, and it has a THD+N of 0.0012% and a SNR of 118 dB.
I tested the ST2 Pro Nebula with my Google Pixel 7 Pro and the volume is way too high even when setting it to minimum. I used Symphonium, which allows to set preamplification up to -15 dB, and even then I found it too high. On a PC I had to reduce the volume both in the system panel and in the application itself.
Sound & Specs
I tested the Hidizs ST2 Pro Nebula with my Google Pixel 7 Pro smartphone, as well as an HP Spectre X13 laptop.
Hidizs ST2 Pro Nebula |
| Frequency response | 20 – 40,000 Hz |
| Impedance | 32 Ω |
| Sensitivity | 108 dB |
With an impedance of 32 ohm and a sensitivity of 108 dB, the ST2 Pro Nebula only need a single mW to sound unbearably loud, so the 70 mW afforded by the Nebula DAC are way more than enough.
The soundstage offers good width, which extends to the sides like a large room, but there is virtually no depth. Instruments that appear in the centre sound like they are inside your head, rather than in front of you, in a way that’s much more pronounced than with other earphones. Imaging is very good as instruments are placed with great accuracy on the stage, each with its own clearly-defined place. Instrument separation is decent, although even moderately complex tracks can become a bit confused.
As the ST2 Pro Nebula follow the Harman 2019 target curve, bass is relatively abundant. It is mostly concentrated in the mid-bass area so depth is limited, but sufficient to hit around 60 Hz and therefore to give that “oomph” to music; bass-heavy tracks like Perturbator’s Disco Inferno sound convincing enough, although the deeper, more physical notes are out of reach. There’s a good level of detail, however in layered tracks this often gets lost in the mix.
Midrange is overall prominent and very clearly present in the mix; although it sits behind treble, it is in front of bass. In terms of internal balance, midrange is relatively bright thanks to a slight emphasis on the upper area, so that instruments like trumpets and violins are slightly further forward in the mix than the rest. Overall, however, midrange sounds a bit compressed and dull: as an example, you can take the piano around the 6:00-6:30 mark in Snarky Puppy’s Flood, which sounds flat. This is due to the area around 1 kHz being slightly recessed. This has an impact on voices, too: in both Janis Joplin’s As Good as You’ve Been to This World and Steely Dan’s Deacon Blues, the voices sound distant and muffled; raising the 1-1.5 kHz area by 3 dB makes them much clearer and more natural sounding. Detail is very good overall, although in complex tracks (just like with bass) it gets lost.
Treble sports very good extension, especially for the price range. It is relatively linear overall, but it does have one issue: there is a relatively large spike between 8 kHz and 10 kHz, which makes some instruments very prominent and, in some cases, a bit fatiguing: as an example, in Ulver’s Nemoralia, the cymbals are very prominent and sharp, and there is a hiss in the background during the chorus which is very intense and unpleasant; a similar thing happens with Snarky Puppy’s White Cap, where the cymbals are quite sharp. The level of detail is sufficient.
Final Thoughts
When judging a product, price is of paramount importance and can make or break it. In the case of the Hidizs ST2 Pro Nebula, price is definitely working to its advantage: at $60, it is almost a steal. You get a very decent pair of earphones, plus a USB DAC-cable which you can use with other earphones as well and which has enough power to drive most earphones and many low-impedance headphones, too. While the ST2 Pro Nebula aren’t super linear, nor super detailed nor technical, they do everything well enough that they’re satisfying to use. And with the current trend of removing jack sockets from phones, earphones like these are the future – as they’re more convenient than attaching a DAC to your phone if you want to avoid wireless earbuds.
Overall, I think that the Hidizs ST2 Pro Nebula are a very good product which is well worth the money it costs. They’re nice earphones for those who are starting their audio journey, or for anyone who wants the practicality of a cable without the expense of a dedicated DAC for their phone, while still getting good sound quality.
